Systems for producing stereoscopic images, that is images which appear to have depth when viewed generally consist of a method and/or apparatus for creating two images which are recorded from different perspectives so that when displayed one eye sees one perspective of the image and the other eye sees a different perspective of the image. Most commonly this is accomplished by the utilization of two or more cameras which are spaced apart and which record an image from different perspectives. The images form each camera are then disposed side by side, such as on film or on a cathode ray tube. Means, such as polarized or photopic/scotopic glasses, special screens or special apparatus for timing the display of the left and right images, are provided so that the left eye sees only one image and the right eye sees only the other image while to the viewer the image appears to have depth. An example of such a system is found in U.S. Pat. No. 3,784,738 issued Jan. 8, 1974 to Howard Natter. The subject matter of the '738 patent relates to the production of stereoscopic video images employing an image displacer which creates two images as viewed from different perspectives. As an alternative, Natter may employ two spaced apart video cameras to create two images of the scene. Special headgear having spaced apart viewing windows so that only one eye can view one image is required for viewing the stereoscopic images. The system relies heavily on the fact that the images must be perfectly synchronized when 12 shot and when viewed to avoid image deterioration.
Similarly, U.S. Pat. No. 4,303,316, issued Dec. 1, 1981 to Robert McElven, discloses a two-camera system for recording left and right perspectives of a scene. The images are combined on a film strip in a sequence of left and right views with non-moving parts of the scene superimposed. In this manner stereoscopic images on a two dimensional surface can be seen with the unaided eye. As an alternative, a single camera having a shutter that alternately records left and right perspectives of the scene can be used.
Other systems employing several cameras or optical means for creating left and right image perspectives which are then displayed alternatively to create a stereoscopic effect are disclosed in U.S. Pat. No. 3,251,933, issued May 17, 1966 to H. E. Beste; U.S. Pat. No. 4,523,226, issued Jun. 11, 1985 to Lipton, et al.; U.S. Pat. No. 5,142,642, issued Aug. 25, 1992 to H. Sudo; and U.S. Pat. No. 4,751,750 issued Jun. 14, 1988 to M. Robinson.
Another method for producing stereoscopic images on a two dimensional display involves moving the camera and image with respect to one another to produce stereoscopically related images. These images can be displayed sequentially to provide a stereoscopic image without the aid of a viewing device. Alternatively, a viewing device can be used which, in effect, causes the left eye to see a left perspective and the right eye to see a right perspective of the image. These systems allow for the use of a single camera. For example, in U.S. Pat. No. 4,807,024, issued Feb. 21, 1989 to McLauren et al., a single camera is mounted on a moving the platform and the stereoscopically related images are presented alternately to the viewer so that the resulting image is perceived by the viewer as having depth. No special viewing device or glasses is required. U.S. Pat. No. 4,754,327, issued Jun. 28, 1988 to Thomas Lippert, also employs a single camera on a horizontally moving platform for producing left and right perspectives of an image as the camera moves. The image may be displayed as separate frames for the left and right eye to provide depth to the image. The images may be separated by differences in polarity of light or presented sequentially to the left and right eye of the viewer.
As an alternative to moving a camera with respect to the image, moving mirrors can be utilized to essentially move the image with respect to the lens so that alternate perspectives of the image are recorded. For example, U.S. Pat. No. 4,723,159, issued Feb. 2, 1988 to Donald Imsand, combines a reference camera and a moving dynamic camera to produce stereoscopic images. As an alternative to moving the dynamic camera, Imsand may utilize rotating mirrors to create the effect of moving the dynamic camera, although two cameras are required.
U.S. Pat. No. 5,151,821, issued Sep. 29, 1992 to Mortimer Marks, uses the horizontal movement of pair of mirrors arranged at an angle to deflect the image onto the lens of a single camera to create different perspectives of an image as the mirrors move. These images may then be viewed as a stereoscopic image through photopic/scotopic filters. The images appear as conventional two-dimensional images when viewed without the filters.
While the foregoing mirror arrangement does allow for the use of a single camera, the mirrors traveling in a generally horizontal fashion result in dead spaces in the film when the mirrors complete travel in one direction and begin traveling in the opposite direction. Mortimer recognized this problem and disclosed in one embodiment of the invention, a dual camera arrangement utilizing dual sets of moving mirrors so that images were recorded only when the mirrors were moving in one direction. In this manner, the mirrors may be moving from left to right for one camera which is in the recording mode while second camera is shut down to allow its mirrors to return to the left position. When the mirrors of the one camera reach the full right of travel, it shuts down and the second camera begins recording and its mirrors begin moving left to right. In application Ser. No. 617,478, filed Mar. 15, 1996 by Eddie Paul, the problem of dead spots was overcome by the provision of apparatus which is attached to a single, conventional camera. This apparatus comprises a pair of spaced apart mirrors which rotate about the longitudinal axis of the lens and which are arranged to deflect the image from one mirror to the second mirror and thence to the lens to achieve a stereoscopic image.
The use of moving mirrors, either in a circular path or in a horizontal path, provides several disadvantages. First, the use of moving mirrors causes light loss of one f stop or more resulting in a loss of about five to fifteen percent of the available light. In addition, the lens cannot be utilized in a wide angle since the image would be wider than the mirrors at certain points of the rotation. Vibration is also amplified as well as any distortion in either of the mirrors or distortion due to imperfect mounting or travel of the mirrors.